Apparatus and techniques for computerized printing

ABSTRACT

An integrated computerized system for use in color printing having at least one digital representation of a color characteristic of at least one page to be printed and a digital storage memory for storing the digital representation. An imposition apparatus is connected to the storage memory to receive the digital representation and arrange the digital representation in accordance with a desired plate layout, thereby to define a plate image. A press set-up device extracts from the plate image the color characteristic and provides ink flow set-up data to a printing press in accordance with the extracted color characteristic.

FIELD OF THE INVENTION

[0001] The present invention relates to printing and graphic artsgenerally and more particularly to apparatus for page composition andprinting and apparatus for printing control.

BACKGROUND OF THE INVENTION

[0002] The production of a book or magazine involves a large number ofprocesses. The processes may be grouped into five general categories:prepress, plate preparation, press set up or “make ready”; press controloperations; and postpress operations.

[0003] In prepress, the principal processes are graphics, image and textediting and composition. In recent years, this area has undergonerevolutionary changes through application of computer technology. Stateof the art systems for graphics and image editing and composition, aswell as the specific functions of scanning, image processing andplotting include systems manufactured and sold by Scitex CorporationLtd., Herzlia, Israel, such as, respectively, the systems sold under thetrademarks Smart Scanner, Assembler and Raystar.

[0004] Plate preparation involves a technique known as imposition orsignature assembly, which refers to the arrangement of pages on a filmused to produce a printing plate. The present state of the art insignature assembly is the use of large and expensive machinery requiringhighly skilled operators. Presently available signature assemblymachinery involves the following steps: exposure of each of a pluralityof separations (such as C, M, Y and K) for each of a plurality of pagesto be arranged on a single plate; and subsequently, for each separation,such as C, feeding the exposed plurality of pages to an expose andrepeat device such as the Misomex Master S Series, commerciallyavailable from Misomex North America Inc., Rosemont, Ill. The expose andrepeat device is operative to arrange the plurality of exposed Cseparations, corresponding to the plurality of pages to be arranged on asingle plate, at precisely determined positions on a film and toreproduce the C separations at the precisely determined positions by aphotographic process.

[0005] The C printing plate is produced by contact exposure of the film.The signature is proofed prior to exposure of the plate. The plate, onceexposed, is often found to be imperfect and therefore generally requiresquality inspection and defect repair processes. The plate preparationprocess is repeated in order to produce M. Y and K plates.

[0006] Press set-up or “make-ready” takes place after preparation of theprinting plate, and involves scanning of each printing plate to obtaininformation necessary for press set-up. This information includes thevariation of the dot percentage over each plate, which determines therequired ink flow for that plate.

[0007] Press control involves adjustments to the printing press whichare normally made by a pressman examining the printed output from thepress or by automatic press control systems such as the SPM 700,commercially available from Gretag Data and Image Systems,CH-Regensdorf, Switzerland. Automatic press control systems areoperative to scan the printed output from the press compare it to areference, such as a signature proof, and make suitable adjustments tothe printing press. Post press processes include the folding, cuttingand binding of the press output.

[0008] A great number of patents exist in the area of prepress. Theseinclude co-assigned U.S. Pat. No. 4,456,924 which describes method andapparatus for screen generation, co-assigned U.S. Pat. No. 4,853,709which describes an internal drum laser plotter, and co-assigned U.S.application Ser. No. 044,428 which describes a color digital scanner.

[0009] Various processes in the production of printed matter arediscussed in the following publications, the disclosures of which areincorporated herein by reference:

[0010] Alfred Furler, Folding in Practice, in collaboration with STAHLGMBH & Co., 3rd Edition, Germany, 1983;

[0011] William Schreiber, Fundamentals of Electronic Imaging Systems,Springer-Verlag, New York, 1986;

[0012] R. K. Molla, Electronic Color Separation, RK Publications, 1988;and

[0013] Michael H. Brill (Ed.), Perceiving, Measuring and Using Color,SPIE Proceedings, Vol. 1250, Billingham, Wash., USA, February 1990;

[0014] Robert A. Ulicheney, Digital Halftoning and PhysicalReconstruction Function, Ph.D. Thesis, Massachusetts Institute ofTechnology, MA, USA, June 1986; and

[0015] Raymond Blair and Charles Shapiro (Eds.), The Lithographer’sManual, GATF, USA, 1980.

[0016] A state of the art printing press is described in U.S. Pat. No.4,936,211 to Pensavacchia et al. Pensavacchia et al mention printingapparatus which is intended to achieve complete computer control overthe entire printing process, including plate generation, ink regulationand the start-up, print, hold, shut-down and clean-up stages of theactual printing operation. Pensavacchia et al also refer to a pressincluding a workstation which allows an operator to input arepresentation of an original picture to be printed. The workstation mayinclude a CRT display and internal memory for storing image data so thatthe impression to be printed may be previewed before printing and akeyboard via which the operator may key in instructions regarding theparticular press run such as the number of copies to be printed or thenumber of colors in the printed copies. The workstation also is intendedto allow complete control over the operating modes of the pressincluding printing plate imaging, press startup procedure, ink flowregulation, dampening, print, pause and shutdown and clean-up sequences.

[0017] Computer technology has also been proposed for use infacilitating certain stages of the imposition process as described inEuropean Published Patent Application 0309196, published Mar. 29, 1989,European Published Patent Application 0348908, published Jan. 3, 1990and in U.K. Patent 2128843, published on May 2, 1984. U.S. Pat. No.4,150,991 describes one type of optical imposition machine employingtransparencies.

SUMMARY OF THE INVENTION

[0018] The present invention seeks to provide an integrated computerizedsystem for carrying out multiple stages of a printing process. Inaccordance with a preferred embodiment of the invention, the integratedcomputerized system is capable of carrying out functions in all stagesof the printing process from pre-press to press control.

[0019] There is thus provided in accordance with a preferred embodimentof the present invention an integrated computerized system for use inprinting including apparatus for providing at least one digitalrepresentation of at least one page, digital storage apparatus forstoring the at least one digital representation of the at least onepage, imposition apparatus for receiving at least one digitalrepresentation of at least one page and arranging the at least onedigital representation of the at least one pages in accordance with adesired plate layout, thereby to define a plate image, and press set-upapparatus for extracting from the at least one digital representation ofat least one page and providing to a printing press, press set-up data.

[0020] There is also provided in accordance with a preferred embodimentof the present invention an integrated computerized system for use inprinting and including apparatus for providing at least one digitalrepresentation of at least one page, digital storage apparatus forstoring the at least one digital representation of at least one page,imposition apparatus for receiving the at least one digitalrepresentation of at least one page and arranging the at least onedigital representation of at least one page in accordance with a desiredplate layout, thereby to define a plate image, and press controlapparatus for automatically monitoring the printed output of theprinting press and automatically providing adjustments to printing pressregistration and ink flow controls in accordance therewith.

[0021] Further in accordance with a preferred embodiment of the presentinvention, the system also includes press control apparatus forautomatically monitoring the printed sheet provided by the printingpress and for providing adjustments to printing press registration andink flow controls in accordance therewith.

[0022] Still further in accordance with a preferred embodiment of thepresent invention, the at least one digital representation of at leastone page includes a plurality of digital representations of acorresponding plurality of pages.

[0023] Additionally in accordance with a preferred embodiment of thepresent invention, the at least one digital representation of at leastone page includes at least one digital representation of a signaturemarking.

[0024] Still further in accordance with a preferred embodiment of thepresent invention, the at least one digital representation of asignature marking includes a digital representation of a control strip.

[0025] Additionally in accordance with a preferred embodiment of thepresent invention, the apparatus for providing includes editingapparatus for receiving at least one of text and graphics and providingan edited page layout.

[0026] Further in accordance with a preferred embodiment of the presentinvention, the editing apparatus includes a scanner and/or a workstationreceiving an input from a scanner and operator inputs and beingoperative to provide a digitally storable page layout.

[0027] Still further in accordance with a preferred embodiment of thepresent invention, the press set-up apparatus includes data baseapparatus for taking into account characteristics of at least one ofinks and substrates to be used by the press.

[0028] Additionally in accordance with a preferred embodiment of thepresent invention, the press set-up apparatus also includes apparatusfor taking into account characteristics of the press.

[0029] Further in accordance with a preferred embodiment of the presentinvention, the press control apparatus includes apparatus for extractinginformation from the at least one digital representation of at least onepage, apparatus for comparing a press output to the extractedinformation, and apparatus for adjusting the press in accordance with anoutput indication provided by the apparatus for comparing.

[0030] There is also provided in accordance with yet a further preferredembodiment of the present invention an integrated computerized systemfor use in process and monochrome color printing and including apparatusfor providing at least one digital representation of at least one page,digital storage apparatus for storing at least one digitalrepresentation of at least one page, imposition apparatus for receivingat least one of the at least one digital representations of at least onepage and arranging the at least one digital representation of at leastone page in accordance with a desired plate layout, and automatic screencharacteristic selection apparatus operative to select at least onescreen characteristic for each of a plurality of regions defined withinat least one separation of the at least one digital representation of atleast one page.

[0031] Further in accordance with a preferred embodiment of the presentinvention, the system includes automatic screen characteristic selectionapparatus operative to locally select at least screen angles for each ofat least one region in the plate layout based on the color content ofthe at least one region.

[0032] Still further in accordance with a preferred embodiment of thepresent invention, the imposition apparatus includes apparatus forproviding a digital representation of the plate image and plate qualitycontrol apparatus for comparing the digital representation of the plateimage to information extracted from the printed sheet provided by theprinting press.

[0033] According to still a further preferred embodiment of the presentinvention, there is provided imposition apparatus including apparatusfor receiving at least one digital representation of at least one page,apparatus for receiving a desired plate layout, and apparatus forproviding a digital representation of a plate image corresponding to theat least one digital representation of the at least one page arranged inaccordance with the desired plate layout.

[0034] Further in accordance with a preferred embodiment of the presentinvention, the apparatus for receiving includes apparatus for receivingonly a portion of at least one digital representation of at least onepage and the apparatus for providing a digital representation includesapparatus for providing a digital representation of a portion of theplate image in accordance with the desired arrangement of the at leastone page portion on the portion of the plate.

[0035] Still further in accordance with a preferred embodiment of thepresent invention, the imposition apparatus includes apparatus forreceiving at least one digital representation of at least one page,apparatus for receiving information pertaining to a desired platelayout, and apparatus for providing a digital representation of a plateimage corresponding to the at least one digital representation of the atleast one page arranged in accordance with the desired plate layout.

[0036] Additionally in accordance with a preferred embodiment of thepresent invention, the information includes at least informationregarding folding characteristics and/or information regarding cuttingcharacteristics, and/or information regarding binding characteristics.

[0037] Still further in accordance with a preferred embodiment of thepresent invention, the at least one digital representation of at leastone page includes a plurality of digital representations of acorresponding plurality of pages and the imposition apparatus alsoincludes apparatus for modifying the format of at least one of theplurality of digital representations of pages.

[0038] Additionally in accordance with a preferred embodiment of thepresent invention, the apparatus for receiving information includesapparatus for providing a proof of at least the plate image and/or theplate layout.

[0039] Further in accordance with a preferred embodiment of the presentinvention, the proof of the plate image includes an analogrepresentation of the content of the at least one page derived from thedigital representation of the content of the at least one page.

[0040] Still further in accordance with a preferred embodiment of thepresent invention, the plate image includes a digital representation ofat least one signature marking.

[0041] There is also provided in accordance with a preferred embodimentof the present invention color separation generating apparatus includingapparatus for generating a color separation, the color separationdefining a plurality of regions characterized in that at least onescreen characteristic within a first individual one of the plurality ofregions differs from the at least one screen characteristic within asecond individual one of the plurality of regions.

[0042] There is further provided in accordance with a preferredembodiment of the present invention automatic screen characteristicselection apparatus including apparatus for inspecting at least aportion of a representation of a color image, and apparatus forreceiving an output indication from the apparatus for inspecting andusing the output indication to select at least one screen characteristicfor at least a portion of at least one separation of the color image.

[0043] Further in accordance with a preferred embodiment of the presentinvention, the apparatus for inspecting is operative to inspect aportion of a color image and the apparatus for receiving is operative toselect at least one screen characteristic for the corresponding portionof at least one separation of the color image.

[0044] Still further in accordance with a preferred embodiment of thepresent invention, the apparatus for receiving includes apparatus forselecting, for at least one separation of the color image, at least onescreen characteristic for each of a plurality of regions of the colorimage such that the at least one screen characteristic within a firstindividual one of the plurality of regions differs from the at least onescreen characteristic within a second individual one of the plurality ofregions.

[0045] Additionally in accordance with a preferred embodiment of thepresent invention, the representation of the color image includes adigital representation of the color image.

[0046] Further in accordance with a preferred embodiment of the presentinvention, the at least one screen characteristic includes at least ascreen angle, and/or a screen dot shape.

[0047] Still further in accordance with a preferred embodiment of thepresent invention, the apparatus for inspecting includes apparatus forinspecting the color content of at least a portion of a representationof a color image and the apparatus for receiving includes apparatus forselecting at least one screen characteristic for at least one separationof the color image according to the color content of the portion of therepresentation of the color image.

[0048] There is further provided in accordance with still a furtherpreferred embodiment of the present invention signature characteristicunification apparatus including apparatus for inspecting at least aportion of a representation of a signature, and apparatus for modifyingat least one image characteristic within at least one region of therepresentation of the signature, thereby to unify the at least one imagecharacteristic over at least a portion of the signature.

[0049] There is also provided in accordance with a preferred embodimentof the present invention, signature characteristic unificationapparatus, the signature including a representation of a plurality ofpages, the apparatus including apparatus for modifying at least onerepresentation characteristic within at least one region of at least onefirst page from among the plurality of pages, thereby to unify the atleast one image characteristic relative to at least one region of atleast one second page from among the plurality of pages.

[0050] Further in accordance with a preferred embodiment of the presentinvention, the at least one representation characteristic includes atleast one color characteristic.

[0051] Still further in accordance with a preferred embodiment of thepresent invention, the at least one representation characteristicincludes at least one spatial characteristic.

[0052] Additionally in accordance with a preferred embodiment of thepresent invention, the at least one spatial characteristic includes aresolution of a color image.

[0053] There is also provided in accordance with a preferred embodimentof the present invention an image reproduction method including thesteps of providing a representation of an image, the representationincluding a digital indication of at least one location whose appearanceis to be maintained, reproducing the image so as to automaticallymaintain the appearance of the location.

[0054] Further in accordance with a preferred embodiment of the presentinvention, the representation of the image includes a digitalrepresentation of the image and the step of reproducing includes thestep of providing the digital representation of the location toapparatus for reproducing the image.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will be understood and appreciated morefully from the following detailed description, taken in conjunction withthe drawings in which:

[0056]FIG. 1 is a simplified block diagram illustration of an integratedcomputerized system for use in printing constructed and operative inaccordance with a preferred embodiment of the present invention;

[0057]FIG. 2 is a flowchart of a preferred embodiment of a “first pass”algorithm useful in implementing digital signature assembly generator 16of FIG. 1 and comprising a procedure for file reading and rearrangingand for screen angle processing;

[0058]FIG. 3 is a flowchart of a non-rotating block providing procedureuseful in conjunction with the algorithm of FIG. 2;

[0059]FIG. 4 is a flowchart of a rotating block providing procedureuseful in conjunction with the algorithm of FIG. 2;

[0060]FIG. 5 is a flowchart of a preferred embodiment of a “second pass”algorithm useful in implementing digital signature assembly generator 16of FIG. 1 and comprising a procedure for providing digital signatureinformation to screen generator 20 of FIG. 1;

[0061]FIG. 6 is a flowchart of a preferred embodiment of the screensubroutine of step 66 of the flowchart of FIGS. 3; and

[0062]FIG. 7 is a preferred embodiment of the subroutine of steps 124and 130 of FIG. 5.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0063] The following terms, employed herein, are intended to have themeanings specified hereinbelow:

[0064] Color image: This term is intended to include image comprisinggradations of a single tone, such as black and white images.

[0065] Analog representation of a color image: Any representation of acolor image which resembles the original color image. The representationmay appear upon a printed page, a proof or any other suitable substrate.

[0066] Digital representation of a color image: Any representation of acolor image which is expressed in discrete symbols, such as a computerfile.

[0067] Color characteristics of a color image: The characteristics ofthe color image defined by individual elements of a representation of acolor image which directly represent a color or a component of a color.

[0068] Spatial characteristics of a color image: Characteristicsdefining the arrangement of and the relationship between elements of arepresentation of a color image, such as pixels, which characteristicsdo not directly represent a color or a component of a color. Spatialcharacteristics include but are not limited to resolution and formatcharacteristics such as pixel by pixel encoding.

[0069] Digital output device: Apparatus which inputs a digitalrepresentation of a color image and converts it into an analogrepresentation thereof, such as but not limited to a plotter or proofer.The analog representation may be provided on any suitable substrate suchas a hard copy proof, film or plate.

[0070] Reference is now made to FIG. 1, which illustrates an integratedcomputerized system for use in printing constructed and operative inaccordance with a preferred embodiment of the present invention andincluding apparatus 10 for providing a plurality of single page digitalrepresentations 12. Apparatus 10 typically comprises at least oneconventional computerized page layout and assembly system, such as theAssembler workstation commercially available from Scitex Ltd.Alternatively, non-Scitex products such as Illustrator and Photoshop,both commercially available from Adobe, and Freehand, commerciallyavailable from Aldus may be employed in conjunction with an interpreterdevice such as PS-Bridge, commercially available from Scitex.

[0071] One or more such computerized page layout systems may be providedor linked to the system of the present invention by any suitable datacommunication technique or means, and may be remotely located from therest of the system, as desired. Alternatively, the single-page digitalrepresentations may arrive from a large storage device such as a disk.

[0072] Color and spatial basis unification apparatus 14 receives theplurality of single-page digital representations from apparatus 10, eachof which may have different spatial and color characteristics. Color andspatial basis unification apparatus 14 unifies the spatial and colorcharacteristics of the single-page digital representations and outputsdata for each of the single pages which preferably comprisespixel-interleaved data. Preferably, the single-page data is stored inintermediate storage and is subsequently provided to digital signatureassembly generator 16 as explained below with reference to FIG. 3.

[0073] The term “pixel-interleaved data” is defined in Appendix A,attached hereto.

[0074] Color and spatial unification apparatus 14 may comprise aTrans/4,commercially available from Scitex Corporation, Herzlia, Israel, oralternatively may comprise the color and spatial transform apparatusdescribed in Israel Patent Application No. 96957, the disclosure ofwhich is incorporated herein by reference.

[0075] The unified page data provided by color/spatial unificationapparatus 14 is provided to a digital signature assembly generator 16.Digital signature assembly generator 16 is operative to provide adigital representation of the signature by carrying out a fullcomputerized page imposition function on the unified page data,including provision of signature markings such as registration marks,folding marks, cutting marks, control strips, as will be described indetail hereinbelow, preferably resulting in a complete digitalrepresentation of the full signature.

[0076] Signature markings are preferably provided as digital files,which are substantially analogous to the image files. The signaturemarking files are positioned within the signature along with the imagefiles.

[0077] Preferably, the digital signature assembly generator 16 includesa “data” double buffer including two buffers, each of which is largeenough to store the digital representation of one single separation of asignature corresponding to the data required for the exposure of an areacovered by one laser beam path. At any given time, one of the twobuffers of the “data” double buffer provides a first line to a digitaloutput device 22 via screen generator 20 and the other one of the twobuffers loads the line next to be provided to the digital output device22 via screen generator 20.

[0078] Digital signature assembly generator 16 also preferably providesscreen control parameters. The screen control parameters may comprise,for each of a plurality of regions defined within the pages in thesignature, a plurality of parameters relating to screen anglescorresponding to the plurality of separations. A plurality of screenangles corresponding to a plurality of separations in which a colorimage is represented is termed herein “a screen angle quartet”. However,it is appreciated that the number of separations be used to representthe color image need not be 4, but rather may also be any other suitablenumber such as 3.

[0079] Preferably, each screen angle quartet is represented by asuitable code indication, termed herein a “screen control code value”.For example, the code value “1” may represent the screen angle quartet(0, 15, 30, 60), the four components representing the screen angle indegrees for the C, M, Y and K separations respectively. The code value“2” may represent the screen angle quartet (30, 0, 15, 60). A LUT insignature assembly generator 16 may be used to convert the code valuesto screen angles according to separation.

[0080] Preferably, the digital signature assembly generator 16 includesa “regions” buffer. The screen control data for each signature linetypically comprises a plurality of screen angle quartets correspondingto the plurality of regions and, for each region, the byte count ornumber of pixels over which the region extends in the laser pathdirection. For each path within the signature which overlaps at leastone new region, the screen control code for the new region is convertedto screen angle according to separation and all relevant screen controlparameters are loaded into screen generator 20 with the byte counts ofthe regions and of the spaces between them.

[0081] The digital signature assembly generator 16 preferably receivesat least operator inputs via a signature assembly workstation 18.Signature assembly workstation 18 may comprise a computer, such as apersonal computer, running a commercially available impositioningplanning software package such as Impostrip, commercially available fromUltimate Technologies Inc., 4980 Buchan St. Suite 403, Montreal, QuebecH4P 158, Canada. Signature assembly workstation 18 is also preferablyoperative to perform the other functions described below.

[0082] Signature assembly workstation 18 is operative to provide a listof files to be impositioned, preferably including, for each color imagefile and for each signature marking file, information regarding desiredpositioning thereof on the signature. The information regarding desiredpositioning preferably takes into consideration characteristics of thepost-press equipment such as folding, cutting and binding equipment.Therefore, signature assembly workstation 18 preferably storesinformation regarding the post-press equipment. This file list isprovided to digital signature assembly generator 16.

[0083] Preferably, digital signature workstation 18 is operative toreceive from workstation 10 in at least one of digital pages 12 anoperator's selection of crucial zones, termed herein “areas ofinterest”, whose appearances are to be faithfully reproduced. In otherwords, if the digital representation within a particular digital page 12of a particular area of interest is represented by a particular vectorsuch as a vector (C, M, Y, K) then it is desired that, when that area isprinted on the press and subsequently analyzed, the resulting digitalrepresentation of the printed area of interest will remain the same (C,M, Y, K).

[0084] Preferred methods and apparatus for preserving the appearance ofa color image are described in Applicant's co-assigned Israel PatentApplication No. 96957.

[0085] Signature assembly workstation 18 identifies the informationregarding the areas of interest by signature coordinates and providestheir signature coordinates to at least press control device 32.Preferably, the above information regarding areas of interest isincluded in the file list described above.

[0086] The screen control parameters relating to screen angles and thedigital single separation signature output of digital signature assemblygenerator 16 are provided to a screen generator 20, which may comprisethe screen generator incorporated in the Raystar or Dolev plotters,commercially available from Scitex Corporation, Herzlia, Israel. Screengenerator 20 is operative to control the writing apparatus of thedigital output device 22. Screen generator 20 preferably comprises a LUTwhich takes into account characteristics of the press 28 such as dotgain. Digital output device 22 may comprise one or more suitablecommercially available digital output devices suitable for producingseparations of entire signatures, such as the ERAY or Raystar plotters,in which the writing apparatus comprises a laser beam. The resultingsignature separations are exposed, thereby to provide a plurality ofplates 24 corresponding to the plurality of separations, which aremounted on the press 28.

[0087] The digital signature assembly generator 16 is also operative toprovide control data to a press set-up device 26 which is operative toset up or “make ready” the press 28 which produces a printed sheet 30.The press onto which the plate is mounted is typically partitioned intoa plurality of strips, also termed ink-key zones, such as 16, . . . , 28or 32 strips. Preferably, the control data provided to the press set-updevice includes ink flow settings for each strip or ink-key zone. Theink flow setting for each strip may be determined according to theaverage dot percentage within that strip, including the dot percentagescorresponding to any signature marks, such as control strips, partiallyor completely overlapping that strip.

[0088] According to a preferred embodiment of the invention, a proofingdevice 29 may be provided.

[0089] A press control device 32 is preferably provided for inspectingthe printed sheet 30 at at least one location defined by workstation 10and identified by signature co-ordinates by workstation 18 in order toobtain at at least that location an indication of the visual appearanceof the image including at least its color content. This information iscompared with the desired visual appearance information as derived fromthe corresponding digital representation 12 of the at least one page atthe corresponding at least one location designated by workstation 10. Onthe basis of this comparison the press control device 32 may modify asnecessary, on-line, at least one press control parameter such as inkflow so as to improve the visual appearance of the printed product 30.

[0090] Preferably, the press control device is operative to inspect atleast the “areas of interest” selected by the operator. The signaturecoordinates of the areas of interest, as well as their visualappearances are provided to press control device 32 by workstation 18,as described above. The visual appearances of the areas of interest,including the color contents thereof, are compared with thecorresponding desired values transferred by workstation 18. The presscontrol device employs the comparison to modify as necessary at leastone control parameter of press 28, such as amount of ink thereby toincrease the correspondence between the parameters of the areas ofinterest as defined by page layout assembly workstation 10 and betweenthe visual appearance of the areas of interest provided by the press 28.

[0091] Press control device 32 is also preferably operative to receivean indication of the locations and distances between registration marksin order to facilitate synchronization of the press 28.

[0092] Commercially available press set-up devices 26 include, forexample:

[0093] CPC3, by Heidelberg Co., Heidelberg, Germany;

[0094] Roland RCI and CCI, by Man Roland, Offenbach am Main, Germany;and

[0095] PDC Print Density Control, by Komori, Tokyo, Japan.

[0096] Press control device 32 may include a plurality of commerciallyavailable press control systems such as the following:

[0097] SPM 700, by Gretag Data and Image Systems, CH-Regensdorf,Switzerland;

[0098] Calgraph System, commercially available from Celogic,Montpellier, France; and

[0099] Image processor model IP-100, by CC1 Inc., Hackettstown, N.J.,USA.

[0100] The plurality of press control systems typically includes onepress control system per separation.

[0101] The apparatus of FIG. 1 preferably includes a data base, whichmay reside in any suitable location such as the memory of workstation18, which stores preferred combinations of ink, paper and pressparameters. The preferred combinations are preferably combinations whichare known to provide faithful reproduction of color images. The databaseinformation is preferably utilized to modify the operation ofcolor/spatial unification device 14, press set-up device 26.

[0102] The printed sheet provided by the press 28 is then provided topost-press equipment such as folding, cutting and binding equipment,using known techniques, thereby to provide a final printed product whichmay comprise a plurality of printed sheets, such as but not limited to abook, newspaper, or magazine.

[0103] Reference is now made to FIG. 2, which is a generalized flowchart illustrating an algorithm useful in implementing digital signatureassembly generator 16 of FIG. 1.

[0104] As shown in FIG. 2, the first step 50 of the algorithm is toreceive from signature assembly workstation 18 information regarding theorientation of the image represented by a particular digital file suchas its desired position on the page and whether it is to appear uprightor in a rotated orientation such as upside down. This orientationinformation is preferably included in the file list provided byworkstation 18 as described above. The digital file may comprise anindividual one of digital pages 12 or may alternatively comprise a filerepresenting page markings such as registration marks, folding andcutting marks and control strips. The orientation information ispreferably included in the file list provided to digital signatureassembly generator 16 by signature assembly workstation 18.

[0105] A digital representation of a control strip may be generated inthe same way an ordinary image file is generated. Preferred patterns forcontrol strips comprise the patterns of commercially available controlstrips from DuPont (Cromalin process) or from 3M (PrintMatch process).

[0106] Conventional patterns for folding, cutting and registration marksare known and are described in the above-mentioned text, Folding InPractice by Furler.

[0107] In step 51, a plurality of regions is defined which partitionsthe file. The regions may be of uniform size, such as 50 pixels×50pixels. Alternatively, the regions may differ in size, the size of eachregion being a function of the amount of variation of the color valuesof the pixels within that region, such that, within each region, thereis a very small amount of variation between the pixel values.

[0108] Step 52 is to determine, from operator input received viasignature assembly workstation 18, whether the page or file requiresrotation by 180 degrees. The page or file is then stored in blocks,using the non-rotating block providing procedure of FIG. 3, if180-degree rotation is not required, or using the rotating blockproviding procedure of FIG. 4 if 180-degree rotation is required. For aslong as files remain to be processed (step 54), the above process,comprising input step 50, partitioning step 51, decision step 52 and thego-to steps, termed herein “the first pass”, is repeated. Step 54 may beimplemented by referring to the list of files to be impositioned on thesignature which may be provided by a user via signature assemblyworkstation 18 as explained above.

[0109] At the end of the first pass, a second process, termed herein“the second pass” and described herein with reference to FIG. 5, isinitiated for each separation.

[0110] Reference is now made to FIG. 3 which is a flow chart of anon-rotating block providing procedure useful in conjunction with thealgorithm of FIG. 2. As shown, the procedure of FIG. 3 comprises a firststep 60 in which a block index i is initialized and assigned an initialvalue of 1, corresponding to the first block of the page or file beingprocessed.

[0111] In step 62, block i is brought from an individual file from amongthe list of files to be impositioned. The individual file is provided tothe digital signature assembly generator 16 by color/spatial unificationunit 14, as shown in FIG. 1. Block i is stored in a local memory devicesuch as a solid state memory. The block i information stored in thelocal memory device preferably includes the pixel interleaved datadefining the corresponding portion of the color image.

[0112] In step 66, a screen subroutine is performed in which a screenangle quartet, or a screen control code value representative thereof, asexplained above, is computed for each region. The screen subroutine isdescribed in detail hereinbelow with reference to FIG. 6.

[0113] Step 68 is a decision step in which the algorithm branchesdepending on whether the i-th block is the last block or not. If it isnot, then if 4 blocks have accumulated in local memory (step 70), the 4blocks, each of which contain information regarding all four separationsof a portion P of the page, are reorganized (step 72). Each of thereorganized blocks contains information regarding a single separation ofa portion of the page four times as large as P. Step 72 is not performeduntil 4 blocks have accumulated in local memory. The reorganized blocksare stored in a bulk memory unit such as a disk. The block index i isincremented (step 74) and the algorithm is repeated.

[0114] If the block index i in step 68 corresponds to the index of thelast block of the page or other file, the blocks in local memory, whichmay number 1, 2, 3 or 4 blocks, the last of which may not be full, arereorganized (step 76). The blocks in local memory are reorganized into 4complete or partial blocks. The reorganized blocks or partial blocks arestored in a bulk memory unit such as a disk. Step 76 is thereforesimilar to step 72, except that the 4 “separation” blocks are notnecessarily complete blocks.

[0115] Step 76 is followed by step 78, in which screen-angle quartetscomputed for particular regions in step 66 are transferred from “region”local memory to bulk memory.

[0116] Reference is now made to FIG. 4 which is a flow chart of arotating block providing procedure useful in conjunction with thealgorithm of FIG. 2. The procedure of FIG. 4 is similar to the procedureof FIG. 3, analogous steps therefore having been given identicalreference numerals, with the following differences. In FIG. 4,initialization step 60 is replaced by an initialization step 80 in whichblock index i receives an initial value indicative of the last block ofthe page or file.

[0117] Step 80 is followed by step 82 in which block i is brought in andis stored in local memory in reverse. In other words, in the storedblock i, the row order and the pixel order within each row of the blockare inverted, relative to the original block i, since the page or fileis to appear “upside-down” on the plate.

[0118] Step 84, in which screen angle quartets are computed for thevarious regions, is similar to step 66 and is described in detail belowwith reference to FIG. 6.

[0119] Decision step 68 of FIG. 3 is replaced by decision step 86 whichdetermines whether i points to the first block. Index incrementationstep 74 of FIG. 3 is replaced by index updating step 88 in which 1 issubtracted from i.

[0120] As noted hereinabove, when the “first pass” procedure of FIG. 2is completed, a second process, termed herein “the second pass”, isinitiated for each separation, which provides digital informationregarding the entire separation of the signature to screen generator 20of FIG. 1. Preferably, the first and second passes are pipelined.

[0121] Reference is now made to FIG. 5 which is a flowchart of apreferred embodiment of the “second pass” procedure. As shown in FIG. 5,the “second pass” procedures begins with loading step 98 in which thescreen angle quartets computed in step 66 of FIG. 3 or step 84 of FIG. 4are loaded to local memory.

[0122] A laser beam path index initialization step 100 follows, in whichan index k of the laser beam path of the digital output device 22 isinitialized to correspond to the first laser beam path of digital outputdevice 22. In step 102, reference is made to the list of files to beimpositioned, which list includes information regarding desired marginsand the desired arrangement of the pages on the signature, in order todetermine whether laser beam path k will encounter any files or pages.If not, step 104 is operative to clear the entire buffer of the doublebuffer which stores path k, as by filling with zero's. If there arefiles along laser beam path k, a current file index or pointer isdefined to refer to the first file on path k (step 108). In step 110,the offset of the laser beam path k of digital output device 22 of FIG.1 is set with the corresponding coordinate of the first file on path k.Also, the stored information corresponding to the blank or offsetportion of path k is cleared, in order to overwrite obsolete informationfrom previous paths. As explained above, the information regarding pathk is stored in one of the two buffers of the double buffer withindigital signature assembly generator 16.

[0123] Decision step 112 determines whether the current file data forpath k is stored in the local memory. If not, the next block of thecurrent file is brought to the local memory from the bulk memory (step114). The path k data is taken from that block and is stored in anindividual one of the buffers of the double buffer within digitalsignature assembly generator 16 (step 116).

[0124] Decision step 118 determines whether the current file is the lastfile along path k. If not, the gap between the current file and the nextfile along path k, as indicated by the file list, is cleared (step 120).The current file index or pointer is updated to refer to the next fileon path k and the algorithm returns to step 112.

[0125] If the result of decision step 118 is that the current file isthe last file along path k, a subroutine is employed (step 124) which isoperative to output path k−1 (for k>=2). If k=1, steps 124 to 128 arenot performed. A preferred embodiment of the subroutine of step 124 isdescribed below with reference to FIG. 7. The end of path k is marked instep 126. If k is not the last laser beam path (decision step 128), thelaser path index k is incremented and the algorithm returns to step 102.If k is the last laser beam path, the subroutine of FIG. 7 is performedon path k, thereby to provide an output indication of path k.

[0126] The blocks of FIG. 5 define a data organization subalgorithm 140and an output providing subalgorithm 142. Preferably, the outputproviding subalgorithm 142 is pipelined with the data organizationsubalgorithm 140 to allow continuous operation of the digital outputdevice 22. In other words, while the data of path k is being organized,an output indication of path k−1 is being provided.

[0127] Reference is now made to FIG. 6 which illustrates a preferredembodiment of the screen subroutine performed at step 66 of thealgorithm of FIG. 3. As explained above, the screen subroutine of FIG. 6is operative to examine each pixel of block i and compute a screen anglequartet, corresponding to the plurality of separations, for each regionwhose last pixel falls within block i.

[0128] Generally speaking, the screen angle quartet for each region maybe computed as follows: For each region, a plurality of counters ismaintained corresponding to the plurality of code values defined by thescreen code. In other words, each time a pixel within that region isfound to have been assigned a particular screen code value, the countercorresponding to that screen code value is incremented. When all thepixels within the region have been examined, the most frequentlyoccurring screen code value is assigned to the region as a whole and istermed herein the “screen control code”. It is appreciated that anysuitable function may replace the above mode function in computing thescreen control code value of a region as a function of the screen codevalues of pixels within the region.

[0129] The steps of the subroutine may be as follows:

[0130] In step 150, a screen angle quartet, or a screen codecorresponding to a particular screen angle quartet, is assigned to apixel. According to a preferred embodiment of the present invention, thescreen angle quartet of each pixel is a function of the lowest densitycomponent of the pixel value. A sample function for CMYK pixels is asfollows: Lowest density component Screen angle quartet (in degrees) ofpixel value C M Y K C 15 0 30 60 M  0 15  30 60 Y 30 0 15 60 K 60 0 3015

[0131] In step 151, a pixel is stored in the “data” local memory.

[0132] In step 152, the region in which the pixel is included isidentified. In step 154, the counter corresponding to the particularcode value of the pixel, on the one hand, and corresponding to theparticular region, on the other hand, is incremented.

[0133] If the pixel processed above is the last pixel of a region (step156), then a screen control code value corresponding to a screen anglequartet may be assigned to the region (step 158). As explained above,the screen control code value of the region is preferably the screencode value which occurs most in that region. The region screen codevalue may be stored in “region” local memory.

[0134] If the pixel processed above is not the last pixel of the block(step 160), the algorithm, starting from step 150, is repeated for thenext pixel of the block.

[0135] Step 84 of FIG. 4, in which a screen angle quartet is computedfor the various regions, is now described in detail. The subroutine ofstep 84 may be similar to the subroutine of FIG. 6, as described above.However, in step 151, pixels are stored in the “data” local memory inreverse order. Also, in step 158, region screen control code values arestored in the “region” local memory in reverse order.

[0136] Reference is now made to FIG. 7, which is a preferred embodimentof the path outputting subroutine of steps 124 and 130 of the algorithmof FIG. 5. The path outputting subroutine preferably comprises thefollowing steps:

[0137] In step 172, screen control code values are fetched from localmemory for all new regions intersecting the current path of the laserbeam of the digital output device 22 of FIG. 1. The term “new regions”here refers to regions which intersect the current path of the laserbeam but do not intersect the previous path of the laser beam.

[0138] In step 174, each screen control code value is converted into thescreen angle for the current separation or component of the screen anglequartet.

[0139] In step 176 the screen parameters are loaded into screengenerator 20 for each region together with the byte counts correspondingto the region heights and the gap sizes in between regions. An outputindication of the current path of the current separation is provided instep 178.

[0140] Step 180 is a decision step which determines whether the currentpath does or does not intersect any regions which did not intersect theprevious path. If not, in other words, if the regions intersecting thecurrent path are the same as the regions intersecting the previous path,steps 172, 174 and 176 may be bypassed because the screen informationloaded in screen generator 20 is still correct.

[0141] In the present specification, the term “page” is intended toinclude any unit included within a signature which may includerepresentations of an actual page such as a page of a book as well asrepresentations of signature markings and control strips. The term“plate” is intended to refer to any unit of production of a printingdevice such as a press including, but not limited to, a print forme asdefined on page 33 of the above mentioned text “Folding in Practice” byA. Furler.

[0142] It will be appreciated by persons skilled in the art that thepresent invention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the invention is defined onlyby the claims which follow:

1. An integrated computerized system for use in printing and comprising:means for providing at least one digital representation of at least onepage; digital storage means for storing said at least one digitalrepresentation of at least one page; imposition means for receiving saidat least one digital representation of at least one page and arrangingsaid at least one digital representation of at least one page inaccordance with a desired plate layout, thereby to define a plate image;and press control means for automatically monitoring the printed outputof the printing press and automatically providing adjustments toprinting press registration and ink flow controls in accordancetherewith.
 2. Apparatus according to claim 1 and wherein said at leastone digital representation of at least one page comprises a plurality ofdigital representations of a corresponding plurality of pages. 3.Apparatus according to claim 1 and wherein said at least one digitalrepresentation of at least one page comprises at least one digitalrepresentation of a signature marking.
 4. Apparatus according to claim 3and wherein said at least one digital representation of a signaturemarking comprises a digital representation of a control strip. 5.Apparatus according to claim 1 and wherein said means for providingcomprises editing means for receiving at least one of text and graphicsand providing an edited page layout.
 6. Apparatus according to claim 5and wherein said editing means comprises at least one of the followinggroup: a scanner; a workstation receiving an input from a scanner andoperator inputs and being operative to provide a digitally storable pagelayout.
 7. An image reproduction method comprising the steps of:providing a representation of an image, said representation comprising adigital indication of at least one location whose appearance is to bemaintained; reproducing said image so as to automatically maintain theappearance of said location.
 8. An image reproduction method accordingto claim 7 wherein said representation of the image comprises a digitalrepresentation of the image and wherein said step of reproducingcomprises the step of providing the digital representation of saidlocation to apparatus for reproducing the image.